Stereo scanning laser ophthalmoscope

ABSTRACT

An apparatus and method for producing a high contrast, real time, three dimensional representation of a scanned object with the use of an additional scanning mechanism to gain information about the third dimension. A light beam is reflected along an input path and is modified, split, scanned in a first direction, scanned in a second direction, and directed through a stereo base producer to provide stereoscopic information by impinging the beam onto the surface from two different directions. It is then reflected onto the surface whereby the light traverses an output path identical to the input path towards a splitter. Some of the reflected light is directed towards a photodetector coupled to a signal processor to produce an image for real time viewing.

This is a continuation of application Ser. No. 09/555,242 May 26, 2000now U.S. Pat. No. 6,379,006.

The present invention relates to a method and apparatus for thestereoscopic examination of the fundus of the eye. This invention hasapplications in the investigation and diagnosis of diseases that affectthe posterior chamber of the eyeball. The invention will be described inreference to the above application, however, it is possible andenvisioned that the apparatus and technique of the present invention maybe used for stereoscopic imaging in other medical processes.

Visualisation of the ocular fundus can provide important informationabout the state of the eye and of the body. Knowledge regarding ocularand systemic diseases, such as glaucoma, macula degeneration, diabetesor hypertension can be gained from examination of the posterior pole ofthe eye. In the past, imagining of the ocular fundus has been performedthrough the use of an ophthalmoscope, in which a direct view of theretina may be obtained. Other methods include the use of fundus camerasto obtain photographic images. However, these techniques usually requirethe use of mydriatic dilating drugs. The amount of light required toilluminate the fundus may also be uncomfortable for the patient.

Recent developments have resulted in the emergence of a new imaging toolfor the ophthalmologist, in which an image of the eye may be observed inreal-time and captured on a television monitor or screen, duringprocedures such as fluorescein angiography. This instrument, known as ascanning laser ophthalmoscope (SLO), first described in U.S. Pat. No.4,213,678, is currently used to produce representations of the ocularfundus in two dimensions. U.S. Pat. Nos. 4,765,730, 5,268,711 and5,430,509 describe different embodiments of the scanning laserophthalmoscope. All utilise a laser beam or light source that isdirected through the pupil and onto the retina by way of two,directional, scanning mechanisms. The light from the laser is reflectedoff the retinal wall towards a photosensitive detection device.Electro-optical circuitry is employed to convert the light intosynchronized signals, so that it is possible to display an image of thefundus on a television screen or monitor.

U.S. Pat. No. 5,430,509 describes a different embodiment of the scanninglaser ophthalmoscope in which three or more scanning mechanisms areemployed to develop a video image of the fundus. Scanning occurs inthree directions, horizontal, vertical and in the direction of theoptical axis. The inventors suggest that the use of three scanningdevices, each with a different scanning frequency, will reduce thedemands and wear on the scanner's bearings. However, despite the threescanning mechanisms, only a two dimensional image can be reconstructedon screen in real time.

The prior SLO technology described herein above does not permitstereoscopic viewing of the ocular fundus. Nevertheless, the optic discregion and retinal layers have a three dimensional structure.Stereoscopic images of the ocular fundus can impart valuable informationthat cannot otherwise be derived from a two dimensional representation,especially in relation to the diagnosis of glaucoma. Efforts havetherefore been made to create a device capable of producing threedimensional fundus images, while improving on the contrast andresolution of conventional SLO images.

Frambach, Dacey & Sadun (1992, 1993) describe a method of producing athree dimensional fundus picture during fluorescein angiography, using amodified SLO. To obtain stereoscopic data the SLO was manually movedfrom side to side during angiogram proceedings, much like a funduscamera is moved to enable viewing from two different positions.Individual frames from the video tape were chosen from left and rightperspectives to provide a three dimensional image. An alternativeapproach employed by the authors involved the use of a modified Allenseparator. A piece of flat glass was attached to an extended rod,coupled to the Allen separator, so that the glass was interposed betweenthe eye and the SLO. The glass was then rapidly rotated to provide theleft and right perspectives. The resulting frames were digitized bycomputer and viewed directly on a video screen. Superimposed images wereformed by breaking a stereo pair down into corresponding fields andrecombining them to form a single frame. LCD glasses were then used toview the left and right fields with the corresponding eye.

Frambach et al (1993) illustrate that achieving a stereoscopic imagefrom a conventional scanning laser ophthalmoscope is possible. However,the methods involved exhibit a number of disadvantages. Frambach et al'sfirst method of shifting the SLO involved awkward and confusingadjustments, resulting in poor stereoscopic image quality. In the secondmethod, interference due to unwanted back reflections from the Allenseparator would hinder in the transmission of stereoscopic information.Unwanted scattered light would impinge on the photodetecting element,causing a decrease in the contrast and resolution of the images.

Improvements in SLO image resolution and contrast are possible if thedetector receives light only from the plane of interest and notscattered light from the media of the eye. A scanning laserophthalmoscope that could provide high resolution, high contrast imagesof an ocular fundus was realised with the invention of the confocalscanning laser ophthalmoscope (cSLO), such as that described in U.S.Pat. Nos. 5,170,276 and 5,071,246. The confocal SLO utilises a pinholeor slit aperture to focus the light reflected from the fundus onto aphotodetecting element. The aperture is located at a plane in which theopening is conjugate with the plane of the fundus of the eye. In thisway, only the light reflected from the plane of interest impinges on thephotodetecting element and any light scattered or reflected fromout-of-focus planes is prevented from degrading the image.

A further technique to produce three dimensional images of the ocularfundus, known as scanning laser triangulation, is described by Milbocker& Reznichenko (1991). Triangulation is a method commonly used formeasuring distances. Combined with a confocal aperture, this methodinvolves synchronized scanning of a pixel of light across the fundus byway of two mirrors. The illumination and detection paths are arrangedsymmetrically and are defined by the two mirrors. The axial distance ismeasured by the displacement of the illuminated spot in the confocalplane, enabling calculation of the depth. (That is, the points above andbelow the ‘average’ position of the retinal wall). Disadvantages of thismethod include impractical computational speeds for clinical practiceand an inflexible stereo base; large pupil and numerical aperturescannot be used with this technique.

Confocal scanning laser ophthalmoscopes are also currently used toprovide three dimensional information concerning the ocular fundus. Theconfocal aperture of the cSLO allows the user to precisely focus onspecific layers of the retina. By adjusting the focal plane of theaperture, images can be captured at different levels in the fundus, toreproduce desired depth characteristics. In this way a number of“optical sections” can be produced. A computer can then be used toextract depth information, through the process of “stacking” a selectionof the optical sections taken at different levels of the retina.Information regarding the third dimension can therefore be interpolated.

Nevertheless, stereoscopic imaging via the method described is a timeconsuming process. A large number of images must be acquired atdifferent focal planes. Interference from patient head and eye movementis likely to influence the resultant three dimensional image. Computerprocessing times must also be taken into account. These factors-makeconfocal sectioning impractical in a clinical setting, where real timeimages are required for fast diagnosis or treatment.

U.S. Pat. No. 4,900,144 (also see Optics Communications: 87(1,2): 9-14)describes a scanning laser ophthalmoscope that utilises an alternativeconfocal focussing arrangement. The invention is capable of producing athree dimensional representation of an object that displays multiplereflectivity characteristics (such as the ocular fundus) through amethod slightly different from the conventional confocal depthproduction described above. This US patent teaches the use of twoseparate confocal slit apertures and photodetecting units. The detectionslits are orientated parallel to the direction in which the light,reflected from fundus, is scanned. However, both slits are slightlydisplaced from the normal position: the apertures are not conjugate withthe fundus of the eye. One is positioned slightly to the front of theconjugate plane, while the other is placed to the rear. Because of thepositioning of the confocal apertures, the output signals from thephotodetectors vary in intensity according to the unevenness of thefundus. The resultant output signals are processed electronically bydivision calculations, detailed in U.S. Pat. No. 4,900,144, to obtain athree dimensional profile. The resultant real-time image displays thetopography of the fundus through different shade levels, reflectingdifferent retinal depth levels.

Software may also be used to create three dimensional graphic patterns.However, as in the above mentioned case, this method requires a highlevel of computer power to construct the three dimensional image. Anincrease in computer processing time is the inevitable result. It alsorelies on the incorrect assumption of homogeneity of the retinastructures.

The above methods make use of the depth discrimination property, axialresolution, of the confocal system. Unlike the lateral resolution, theaxial resolution is strongly limited by two factors. Firstly, the shapeand size of the laser light focus which is scanned over the retina maysuffer from deformations and distortions, particularly in the directionof the optical axis. This is due to the limited useful numericalaperture of the eye and its' optical imperfections. Furthermore, thesize of the detection pinhole or slit may constrain the axial resolutionof a confocal SLO. Due to intensity limitations on the living eye it isnecessary to provide a detector aperture size which is larger than theoptimal confocal pinhole in order to maintain a sufficient signal tonoise ratio. As a result of these two factors the axial resolution of aconfocal system is typically thirty times less than the lateralresolution.

Accordingly, there remains a need to provide a scanning laserophthalmoscope capable of displaying true stereopsis, which is notrestricted by any of the aforementioned limitations.

It is therefore an object of the present invention to provide animproved method and apparatus for producing a high contrast, real time,three dimensional representation of a scanned object.

It is a further object of the present invention to provide such anapparatus and method with the use of an additional scanning mechanism togain information about the third dimension.

According, therefore, to the present invention, there is provided anapparatus for producing an image of a surface, including:

a laser source for producing a beam of light,

beam modifying means for modifying the properties of the beam,

beam splitting means for splitting the beam,

focussing means for focussing the beam,

first and second scanning means for scanning the beam in first andsecond different directions,

stereo base producing means for obtaining stereoscopic informationconcerning the surface by impinging the beam onto the surface from twodifferent positions, and

reflecting means, wherein a beam from the laser source may be directedalong an input path including being modified with the modifying meansand split by the beam splitting means, directed onto the first scanningmeans to scan the beam in the first direction, directed through thesecond scanning means to scan the beam in the second direction, directedthrough the stereo base producing means, and then directed off thereflecting means and onto the surface, whereby reflected light from thesurface traverses an output path identical to the input path, towardsthe beam splitting means, and whereby some of the reflected light isdirected towards the photodetecting means coupled to the signalprocessing means and display means to produce an image for viewing withvisualising means in real time.

Preferably the apparatus further includes confocal aperture meanswhereby the some of the reflected light is directed through the confocalaperture means towards the photodetecting means. The confocal aperturemeans may include a slit, diaphragm or a pinhole.

Preferably the apparatus includes beam guiding means for guiding thebeam before the beam is directed through the second scanning means, andpreferably the beam modifying means includes a beam expander and/or apinhole aperture.

Thus, although a beam guiding means is unnecessary in someconfigurations, it may be desirable in certain embodiments.

Preferably the apparatus includes a plurality of mirrors for directingthe beam onto the first scanning means.

Thus, although a single mirror and/or lens may be employed, preferablythe apparatus includes a plurality of such mirrors and/or lenses.

Preferably the first and second directions are perpendicular to oneanother, and more preferably one of the first and second directions issubstantially horizontal and the other substantially vertical.

Preferably the surface is the ocular fundus.

The laser source is preferably a helium-neon laser source, a Ti:Sapphirelaser source, an argon-ion laser source or a laser diode source.Preferably the laser source is one of a plurality laser sources.

The beam splitting means may be coated or non-coated.

Preferably the focussing means includes a plurality of mirrors and/orlenses.

Preferably the first scanning means includes a rotating polygon mirror.Alternatively the first scanning means includes an acousto-opticdeflector or a mirror on a resonant scanner or on a galvanometer motor.

Preferably the second scanning means includes a mirror mounted on ascanning galvanometer motor, a resonant scanner or rotating polygonmirror.

Preferably the stereo base producing means is operable to obtainstereoscopic information by directing light onto the surface from adifferent position every alternate frame, and more preferably these twodifferent positions are left and right positions. More preferably thestereo base producing means includes a pair of toggling mirrors fortoggling every alternate frame to image the surface from two slightlydifferent positions, with substantially overlapping imaging areas, tocreate a stereo pair.

Preferably the reflecting means is a large, curved mirror.

Preferably the photodetecting means includes a photomultiplier tube oran avalanche photodiode.

The signal processing means is preferably a computer with a video signalcapture facility, while the display means is preferably a computermonitor or any other suitable display apparatus.

Preferably the visualising means is a pair of Liquid Crystal Display(LCD) goggles or a pair of goggles with a different coloured filter foreach eye.

The present invention also provides a method for scanning a surface witha laser beam to thereby produce an image of the surface, includingdirecting a laser beam along an input path including:

1) modifying and then splitting the laser beam,

2) focussing the beam,

3) scanning the beam in a first direction,

4) scanning the beam in a second direction,

5) directing the beam through stereo base producing means to providestereoscopic information by impinging the beam onto the surface from twodifferent positions, and

6) reflecting the beam onto the surface, whereby reflected light fromthe surface traverses an output path identical to the input path,

splitting the beam and directing a portion of the split beam towardsphotodetecting means coupled to signal processing means and displaymeans, whereby a resultant image may be viewed with visualising means inreal time.

The method preferably includes directing the portion of the split beamthrough a confocal aperture means towards photodetecting means. Theconfocal aperture means include a slit, diaphragm or a pinhole.

Preferably the method includes guiding the beam before scanning the beamin the second direction. The beam guiding is preferably by means of beamguiding means including a curved mirror.

Preferably the first and second directions are perpendicular to oneanother. More preferably one of the first and second directions issubstantially horizontal and the other substantially vertical.

Preferably the surface is an ocular fundus.

Preferably the beam modifying is performed by beam modifying opticsincluding a beam expander and a pinhole aperture.

Preferably the beam modifying optics include a plurality of mirrorsand/or lenses.

Preferably the method includes providing the laser beam by means oflaser source means including a helium-neon laser source, a Ti:Sapphirelaser, an argon-ion laser, a frequency doubled Nd:YAG laser source, afrequency doubled laser diode, or a laser diode.

Preferably the scanning the beam in a first direction is by means offirst scanning means including a rotating polygon mirror.

Alternatively the first scanning means includes an acousto-opticdeflector or a galvanometer mirror or a spinning multifaceted mirror,with the number of facets being a factor of the numbers of lines in thevideo standard, or a resonant scanner.

Preferably the scanning the beam in a second direction is by means ofsecond scanning means including a mirror mounted on a scanninggalvanometer motor, a resonant scanner or rotating polygon mirror.

Preferably the stereo base producing means is operable to obtainstereoscopic information by directing light onto the surface from adifferent position every alternate frame or half frame.

The stereo base producing means preferably includes a pair of togglingmirrors for toggling every alternate frame to image the surface from twoslightly different positions, with substantially overlapping imagingareas, to create a stereo pair. Alternatively, it may include a togglingmirror and be operable to obtain stereoscopic information by adjustingthe phase of the first scanning means. The adjusting may be effectedmechanically or electronically.

Preferably the two positions are left and right positions.

Preferably the reflecting the beam onto the surface is performed bymeans of reflecting means including a large, curved mirror.

Preferably the photodetecting means includes a photomultiplier tube oran avalanche photodiode.

Preferably the signal processing means is a computer with a video signalcapture facility.

Preferably the display means is a computer monitor or any other suitabledisplay apparatus.

Preferably the visualising means is a pair of LCD goggles or a pair ofgoggles with a different coloured filter for each eye.

The present invention also provides an apparatus for visualizing humanor animal tissue including:

laser source means for producing a beam of substantially collimatedlight;

beam modifying means for modifying the beam and/or controllingcharacteristics of the beam;

beam splitting means for splitting the beam;

focussing means for focussing the beam;

first scanning means for scanning the beam in a first direction;

second scanning means for scanning the beam in a second directionsubstantially perpendicular to the first direction, whereby the beam canbe converted into a raster pattern;

means for adjusting beam paths so scanned laser beam or beams approachtissue from different positions;

reflecting means for reflecting the raster pattern;

electro-optical means for controlling the rate of scanning in the firstand second directions and the rate of depth scanning;

photodetecting means for detecting the light reflected from the tissue;

signal processing means for converting the signals into televisionlines;

display means for displaying an image; software means for converting theimage into an interlaced image; and

visualising means for viewing the image in three dimensions in realtime.

Preferably the apparatus includes confocal aperture means forsubstantially eliminating scattered, unwanted light or out of focuslight. The confocal aperture means is preferably a slit, diaphragm orpinhole.

Preferably the apparatus includes beam guiding means for guiding thebeam onto the second scanning means. The beam guiding means preferablyincludes a curved mirror. Alternatively the beam guiding means mayinclude lenses and/or mirrors.

Preferably the laser source means is a helium-neon laser source, aTi:Sapphire laser source, an argon-ion laser source, a frequency doubledNd:YAG laser source, a frequency doubled laser diode, a laser diodesource or any other monochromatic light source.

Preferably the laser source means includes two or more laser sources.

Preferably the beam modifying means includes a beam expander and/or apinhole.

Preferably the second focussing optics includes a plurality of mirrorsand/or lenses.

Preferably the first scanning means includes an acousto-optic deflectoror a resonant or galvanometer mirror or a spinning multifaceted mirror,with the number of facets being a factor of the numbers of lines in thevideo standard (e.g. 5 or 25 for PAL), or a resonant scanner.

Preferably the second scanning means includes a galvanometer mountedmirror, or a resonant scanner or a rotating polygon mirror.

Preferably the stereo base producing means is operable to providestereoscopic information about the surface by directing light onto thesurface from two different positions, alternating every alternate frame,and more preferably the stereo base producing means includes a pair oftoggling mirrors that toggle every alternate frame to image the surfacefrom slightly different positions, with substantially overlappingimaging areas, such that a stereo pair can be created.

Alternatively the one or both of the pair of toggling mirrors may bereplaced by electronic circuitry that can vary the phase of the firstscanning means, or a galvanometer for turning the whole first scanningmeans, a prism or glass plate or any other means that is capable ofdirecting light onto the surface from disparate positions everyalternate frame.

Preferably the reflecting means is a large, curved mirror.

Preferably the electro-optic means is a plurality of electric circuitswith optical or electronic feedback on the scan position of the mirrors.

Preferably the photodetecting means includes a photomultiplier tube, oran avalanche photodiode.

Preferably the signal processing means is a computer with a video signalcapture facility.

Preferably the display means is a computer monitor or any other suitabledisplay monitor. Preferably the software means is an image processingprogram that is capable of producing an interlaced image in real time.

Preferably the visualizing means includes a pair of LCD goggles or apair of goggles with a different coloured filter for each eye.

The tissue may be ocular, which may be the fundus of an eye, in theoptic nerve head region, or any other ocular feature of interest.

Preferably the first direction is substantially horizontal.

In order that the invention be more fully ascertained, some preferredembodiments will be described, by way of example, with reference to theaccompanying drawing in which:

FIG. 1 is a schematic diagram of a first preferred embodiment of thepresent invention;

FIG. 2 illustrates the process of image production; and

FIG. 3 is a schematic diagram illustrating an electrical configurationof one preferred embodiment of the present invention.

Referring to FIG. 1, a preferred embodiment of the present inventionutilises a Helium-Neon laser source 1, or any other suitable source ofsubstantially collimated light, which emits a laser beam 2.Alternatively, two or more laser sources may be utilised to produce beam2. This beam is directed through a focussing system including beamexpanders 3 and 5 (in the form of lenses), which expand the beam to aspecified size, and a pinhole 4 between beam expanders 3 and 5. The beam2 is then reflected from a mirror 6 towards beam splitting means in theform of beam splitter 7. Part of the light passes through the beamsplitter 7 into a light trap 8. The rest of the light is reflectedtowards a number of focussing mirrors 9. Alternatively a lens orcombination of lens and mirrors may be placed at this point. Thefocussing mirrors 9 guide the beam onto a resonant scanner or a rapidlyrotating multiple facet mirror 10, which acts as a horizontal scanner,and subsequently onto a small curved mirror 11, which shapes the beaminto a horizontal line. The beam travels to a vertical scanner 12, inthis case a galvanometer controlled mirror, and is preferably directedonto a pair of toggling mirrors 13 and 14. These mirrors are positionedso that each directs the beam 2 onto the surface-to-be-imaged from twoslightly different positions, with substantially overlapping imagingareas. They preferably toggle every alternate frame, such that visualinformation is received from the right and left perspectives inalternate frames. A second preferred embodiment would position togglingmirrors 13 and/or 14 before the horizontal scanning mechanism 10.Alternatively, the two toggling mirrors could be substituted with asingle mirror that can change position preferably every second frame orhalf frame, or a galvanometer mounted prism or glass plate that iscapable of imaging from the left and right perspective every half frame.Further embodiments include replacing toggling mirrors 13 or 14 withelectronics that can vary the phase of the horizontal scanner or with agalvanometer that can turn the whole horizontal scanner.

The toggling mirrors 13 and 14, or one of the various alternatives,rapidly direct the beam through the pupil of eye 16 from two slightlydifferent positions. The light, now a raster, is reflected off a largecurved mirror 15 before entering the eye. The light that enters the eyethrough the pupil 16 passes through the eye's internal structure toreach the retina at the back of the fundus. The light is reflected offthe retinal layers and travels to the exterior through the pupil. Thereflected beam 17 traverses the same output path as the incident beam 2.Upon reaching beam splitter 7, most of the light continues through thebeam splitter towards focussing means in the form of focussing optic 18.The reflected light is impinged off mirror 19 towards a confocalaperture 20, preferably a slit, although a pinhole configuration is alsosuitable. The beam then enters a photodetector 21, by preference aphotomultiplier tube or an avalanche photodiode. The output of thephotosensor is then preferably converted to a standard television signalpattern through signal processing means 22.

Electro-optic signals are received by an imaging board in computer 23and appropriate electronic hardware and software converts theinformation sent from toggling mirrors 13 and 14 into first and secondimages. An interlaced image of half frames is then constructed on amonitor 24, preferably a computer monitor, in which every line or secondline is captured from both images. Referring to FIG. 2, image A andimage B, either of which may be the left or right image, are combined toform a single image C containing stereoscopic information. The top lineof the interlaced image C is line 1A from, in this example, image A,while the next line down of image C is line 2B from image B. The processof capturing alternate lines from the two images continues until thecompletion of an interlaced image. A three dimensional view can then beperceived by an observer with the use of a pair of liquid crystaldisplay (LCD) goggles 25 coupled to. display means 24 (see FIG. 1). Asthe software writes the information from image A which may be, forexample, the left image, the LCD goggles momentarily shutter theobserver's right eye. A complementary process occurs with image B. Inthis way, the left eye views the left perspective, and the right eyeviews the right perspective, enabling the observer to detect astereoscopic or three dimensional image of the ocular fundus in realtime. Alternatively, an interlaced image can be written so that thelines from image A are one colour, (e.g. green) and the lines from imageB are another (e.g. red). Wearing goggles with matching colour filtersfor each lens (e.g. red and green) allows each eye to perceive one imageonly, and thus view a stereoscopic image.

FIG. 3 illustrates the signal processing involved in controlling thescanning mechanisms. The focussing optics, beam splitter, photodetectorand viewing apparatus have been omitted for simplicity. Correspondingreference numerals are used for like or corresponding parts from theseveral diagrams.

Electro-optic circuitry is employed to detect the beginning and the endof each raster and the end of each image frame. Laser source 1 producesa beam of monochromatic light 2 which is directed onto horizontalscanning mechanism 10. A driver 30, such as a 35000 RPM motor, drivesthe polygon mirror in circles to generate a horizontal line scan.Alternatively, a resonant scanner is driven in a sinusoidal pattern togenerate the horizontal line scan. The line is reflected off mirror 11,and onto another mirror 32, which is driven in a sawtooth patternperpendicular to the motion of the line. The action of 10 and 32together produce a rectangular raster pattern. The timing of the startof the sawtooth pattern is set by the detection of the end or the startof the line at mirror 11. A detector 31 senses the end or start of theline, and this signal is conditioned into a sawtooth by signal processor22. The signal processor 22 counts the number of lines in a raster andgenerates a frame synch. signal 40. A line synch. signal 42 is alsogenerated. Both of these signals are sent to the SLO computer system 23.After the laser beam 2 has been converted into a raster, it is furtherdeflected by the depth producing apparatus, which in this case is shownas prism 34. The signal processor 22 also sends a signal to the prismcontroller 33 to tell it when to move from one position (image A) toanother (image B). The timing of this movement can be varied, buttypically it is at the end of every frame or half frame. The signalprocessor typically sends a square wave. to the controller. The laserbeam is then impinged off mirror 15 and directed through the pupil ontothe retina (not shown). The reflected beam traverses the output pathdescribed in FIG. 1 to the photodetector not shown).

Signal processing means 22, coupled to the photodetector, sendselectro-optic signals to imaging board 35, in computer 23, whereappropriate hardware and software interprets them and constructs image Aand image B as left and right perspectives. An interlaced image, is thencreated by specialized software and displayed on display means 24 (notshown) in real time. LCD goggles or other appropriate viewing means, canthen be used to visualise the three dimensional interlaced image. Thecomputer could also use the angle between the two images to calculatethe real three dimensional shape.

Modification within the spirit and scope of the aforementioned inventionmay be readily effected by a person skilled in the art. Otherembodiments would involve the use of a galvanometer mounted prism orglass plate in place of toggling mirrors to produce images from twodifferent perspectives. Electronics that vary the phase of thehorizontal scanner or a galvanometer that turns the whole horizontalscanner may also be utilised. It is to be understood, therefore, thatthis invention is not limited to the particular embodiments described byway of example hereinabove.

What is claimed is:
 1. An apparatus for producing an image of areflective surface, which image contains stereoscopic information,including: means for producing an incident beam of light, focussingmeans for focussing said incident beam, scanning means for scanning saidincident beam in first and second different directions, stereo baseproducing means for alternately impinging said incident beam onto saidsurface from two different positions as it is scanned over the surfaceby the scanning means; photodetecting means; and means to direct atleast a portion of return light, derived by reflection of said beam fromsaid surface, to said photodetecting means for processing to produce adisplay image for viewing with visualizing means, which image containsstereoscopic information about said surface by virtue of saidimpingement of said beam from two different positions.
 2. An apparatusas claimed in claim 1 wherein said means to direct at least a portion ofsaid return light includes beam splitting means for separating thereturn light from said incident beam.
 3. An apparatus as claimed inclaim 1 further including signal processing means and display meanscoupled to said photodetecting means for effecting said processing ofthe return light and production of said display image.
 4. An apparatusas claimed in claim 1 further including reflecting means for directingsaid beam onto said surface as it is scanned and as it is changedbetween said two different impingement positions.
 5. An apparatus asclaimed in claim 4 wherein said reflecting means is a large, curvedmirror.
 6. An apparatus as claimed in claim 1 further including confocalaperture means positioned so that said return light is directed throughsaid confocal aperture means towards said photodetecting means.
 7. Anapparatus as claimed in claim 6, wherein said confocal aperture meansincludes a slit, diaphragm or a pinhole.
 8. An apparatus as claimed inclaim 1 wherein said means for producing said incident beam includesbeam modifying means in the form of at least one of a beam expander anda pinhole aperture.
 9. An apparatus as claimed in claim 1, including aplurality of mirrors for directing said beam onto said scanning means.10. An apparatus as claimed in claim 1, wherein said first and seconddirections are perpendicular to one another whereby said beam can bescanned in a raster pattern.
 11. An apparatus as claimed in claim 10,wherein one of said first and second directions is substantiallyhorizontal and the other is substantially vertical.
 12. An apparatus asclaimed in claim 1 wherein said means for producing a beam of lightincludes a laser source whereby said beam is a laser beam.
 13. Anapparatus as claimed in claim 12, wherein said laser source is ahelium-neon laser source, a Ti:Sapphire laser source, an argon-ion lasersource, a frequency doubled Nd:YAG laser source, a frequency doubledlaser diode, or a laser diode source.
 14. An apparatus as claimed inclaim 12, wherein said laser source is one of a plurality of lasersources.
 15. An apparatus as claimed in claim 1 wherein said scanningmeans includes one or more rotating polygon mirrors.
 16. An apparatus asclaimed in claim 1, wherein said scanning means includes one or moredevices selected from acousto-optic deflectors, and mirrors on aresonant scanner or on a galvanometer motor.
 17. An apparatus as claimedin claim 1, wherein said stereo base producing means is operable todirect said incident beam onto the surface from a different positionevery alternate frame or half-frame.
 18. An apparatus as claimed inclaim 1, wherein said two different positions from which said incidentbeam is impinged onto said surface are left and right positions.
 19. Anapparatus as claimed in claim 1, wherein said stereo base producingmeans includes a pair of toggling mirrors for toggling every alternateframe to image the surface from two slightly different positions, withsubstantially overlapping imaging areas, to create a stereo pair.
 20. Anapparatus as claimed in claim 1, wherein said photodetecting meansincludes a photomultiplier tube or an avalanche photodiode.
 21. Anapparatus as claimed in claim 1, further including signal processingmeans for effecting said processing of the return light, which signalprocessing means is a computer with a video signal capture facility. 22.An apparatus as claimed in claim 21 further including display means forproducing said display image, which display means is a computer monitoror any other suitable display apparatus.
 23. An apparatus as claimed inclaim 1, wherein said visualizing means is a pair of Liquid CrystalDisplay goggles or a pair of goggles with a different coloured filterfor each eye.
 24. A laser ophthalmoscope comprising apparatus accordingto claim 1 for producing a stereo image of ocular tissue.
 25. A methodfor scanning a surface with an incident beam of light to thereby producean image of said surface, which image contains stereoscopic information,including: directing said incident beam along an input path including:focussing said beam, scanning said beam in a first direction, scanningsaid beam in a second direction, and directing said beam through stereobase producing means to alternately impinge said incident beam onto saidsurface from two different positions as it is scanned over the surfacein said first and second directions; directing at least a portion of thereturn light, reflected from said surface, to photodetecting meanscoupled to signal processing means and display means for processing toproduce a display image for viewing with visualizing means, which imagecontains stereoscopic information about said surface by virtue of saidimpingement of said beam from two different positions.
 26. A methodaccording to claim 25 including separating the return light from saidincident beam.
 27. A method according to claim 25 including reflectingsaid beam onto said surface as it is scanned and as it is changedbetween said two different impingement positions.
 28. A method accordingto claim 27 wherein said reflecting is from a large, curved mirror. 29.A method as claimed in claim 25, including directing said portion ofsaid reflected light through a confocal aperture means towards saidphotodetecting means.
 30. A method as claimed in claim 25, wherein saidfirst and second directions are perpendicular to one another, wherebysaid scanning is in a raster pattern.
 31. A method as claimed in claim30, wherein one of said first and second directions is substantiallyhorizontal and the other substantially vertical.
 32. A method as claimedin claim 25, wherein said surface is ocular tissue.
 33. A method asclaimed in claim 25, wherein said beam modifying is performed by beammodifying optics including a beam expander and/or a pinhole aperture.34. A method according to claim 25 wherein said incident beam is a laserbeam.
 35. A method as claimed in claim 34 including providing said laserbeam by means of laser source means including a helium-neon lasersource, a Ti:Sapphire laser, an argon-ion laser, a frequency doubledNd:YAG laser source, a frequency doubled laser diode, or a laser diode.36. A method as claimed in claim 25, wherein said scanning said beam ina first direction is by means of first scanning means including arotating polygon mirror.
 37. A method as claimed in claim 25, whereinsaid scanning said beam in a first direction is by means of firstscanning means including an acousto-optic deflector or a galvanometermirror or a spinning multifaceted mirror, with the number of facetsbeing a factor of the numbers of lines in the video standard, or aresonant scanner.
 38. A method as claimed in claim 25, wherein saidscanning said beam in a second direction is by means of second scanningmeans including a mirror mounted on a scanning galvanometer motor, aresonant scanner or rotating polygon mirror.
 39. A method as claimed inclaim 25, wherein said stereo base producing means is operable to directsaid incident beam onto the surface from a different position everyalternate frame or half frame.
 40. A method as claimed in claim 25,wherein said stereo base producing means includes a pair of togglingmirrors for toggling every alternate frame to image the surface from twoslightly different positions, with substantially overlapping imagineareas, to create a stereo pair.
 41. A method as claimed in claim 25,wherein said stereo base producing means includes a toggling mirror andis operable to obtain stereoscopic information by adjusting the phase ofsaid scanning in said first direction.
 42. A method as claimed in claim41, wherein said adjusting is effected mechanically or electronically.43. A method as claimed in claim 25, wherein said two differentpositions from which said incident beam is impinged onto said surfaceare left and right positions.
 44. A method as claimed in claim 25,wherein said photodetecting means includes a photomultiplier tube or anavalanche photodiode.
 45. A method as claimed in claim 25, wherein saidsignal processing means is a computer with a video signal capturefacility.
 46. A method as claimed in claim 25, wherein said displaymeans is a computer monitor or any other suitable display apparatus. 47.A method as claimed in claim 25, wherein said visualizing means is apair of Liquid Crystal Display goggles or a pair of goggles with adifferent coloured filter for each eye.
 48. A method as claimed in claim32 wherein said ocular tissue is the fundus of an eye.
 49. A method asclaimed in claim 32 wherein said ocular tissue is the optic nerve headregion.